gNB caracal USRP build: don't stop if we can't reboot

Sometimes the connection fails because of the reboot. Without may_fail,
it would stop the build, which will then run the wrong code, possibly.
Instead, continue; if there is a problem with USRP, it will be visible
when starting nr-softmodem.

ci-scripts/xml_files/gnb_usrp_build.xml

@@ -47,6 +47,7 @@
 	<testCase id="100000">
 		<class>Custom_Command</class>
 		<desc>Reboot USRP</desc>
+		<may_fail>true</may_fail>
 		<node>caracal</node>
 		<command>ssh root@192.168.20.2 reboot</command>
         </testCase>